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// Copyright 2018 The gVisor Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package fragmentation
import (
"math"
"sort"
"gvisor.dev/gvisor/pkg/sync"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/stack"
)
type hole struct {
first uint16
last uint16
filled bool
final bool
// pkt is the fragment packet if hole is filled. We keep the whole pkt rather
// than the fragmented payload to prevent binding to specific buffer types.
pkt *stack.PacketBuffer
}
type reassembler struct {
reassemblerEntry
id FragmentID
memSize int
proto uint8
mu sync.Mutex
holes []hole
filled int
done bool
creationTime int64
pkt *stack.PacketBuffer
}
func newReassembler(id FragmentID, clock tcpip.Clock) *reassembler {
r := &reassembler{
id: id,
creationTime: clock.NowMonotonic(),
}
r.holes = append(r.holes, hole{
first: 0,
last: math.MaxUint16,
filled: false,
final: true,
})
return r
}
func (r *reassembler) process(first, last uint16, more bool, proto uint8, pkt *stack.PacketBuffer) (*stack.PacketBuffer, uint8, bool, int, error) {
r.mu.Lock()
defer r.mu.Unlock()
if r.done {
// A concurrent goroutine might have already reassembled
// the packet and emptied the heap while this goroutine
// was waiting on the mutex. We don't have to do anything in this case.
return nil, 0, false, 0, nil
}
var holeFound bool
var memConsumed int
for i := range r.holes {
currentHole := &r.holes[i]
if last < currentHole.first || currentHole.last < first {
continue
}
// For IPv6, overlaps with an existing fragment are explicitly forbidden by
// RFC 8200 section 4.5:
// If any of the fragments being reassembled overlap with any other
// fragments being reassembled for the same packet, reassembly of that
// packet must be abandoned and all the fragments that have been received
// for that packet must be discarded, and no ICMP error messages should be
// sent.
//
// It is not explicitly forbidden for IPv4, but to keep parity with Linux we
// disallow it as well:
// https://github.com/torvalds/linux/blob/38525c6/net/ipv4/inet_fragment.c#L349
if first < currentHole.first || currentHole.last < last {
// Incoming fragment only partially fits in the free hole.
return nil, 0, false, 0, ErrFragmentOverlap
}
if !more {
if !currentHole.final || currentHole.filled && currentHole.last != last {
// We have another final fragment, which does not perfectly overlap.
return nil, 0, false, 0, ErrFragmentConflict
}
}
holeFound = true
if currentHole.filled {
// Incoming fragment is a duplicate.
continue
}
// We are populating the current hole with the payload and creating a new
// hole for any unfilled ranges on either end.
if first > currentHole.first {
r.holes = append(r.holes, hole{
first: currentHole.first,
last: first - 1,
filled: false,
final: false,
})
}
if last < currentHole.last && more {
r.holes = append(r.holes, hole{
first: last + 1,
last: currentHole.last,
filled: false,
final: currentHole.final,
})
currentHole.final = false
}
memConsumed = pkt.MemSize()
r.memSize += memConsumed
// Update the current hole to precisely match the incoming fragment.
r.holes[i] = hole{
first: first,
last: last,
filled: true,
final: currentHole.final,
pkt: pkt,
}
r.filled++
// For IPv6, it is possible to have different Protocol values between
// fragments of a packet (because, unlike IPv4, the Protocol is not used to
// identify a fragment). In this case, only the Protocol of the first
// fragment must be used as per RFC 8200 Section 4.5.
//
// TODO(gvisor.dev/issue/3648): During reassembly of an IPv6 packet, IP
// options received in the first fragment should be used - and they should
// override options from following fragments.
if first == 0 {
r.pkt = pkt
r.proto = proto
}
break
}
if !holeFound {
// Incoming fragment is beyond end.
return nil, 0, false, 0, ErrFragmentConflict
}
// Check if all the holes have been filled and we are ready to reassemble.
if r.filled < len(r.holes) {
return nil, 0, false, memConsumed, nil
}
sort.Slice(r.holes, func(i, j int) bool {
return r.holes[i].first < r.holes[j].first
})
resPkt := r.holes[0].pkt
for i := 1; i < len(r.holes); i++ {
fragPkt := r.holes[i].pkt
fragPkt.Data.ReadToVV(&resPkt.Data, fragPkt.Data.Size())
}
return resPkt, r.proto, true, memConsumed, nil
}
func (r *reassembler) checkDoneOrMark() bool {
r.mu.Lock()
prev := r.done
r.done = true
r.mu.Unlock()
return prev
}
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